The present invention relates to an adsorbent for lithium and a method for the preparation thereof or, more particularly, to an adsorbent for lithium suitable for the recovery of the lithium value from a low-concentration aqueous solution of lithium by the method of adsorption with excellent selectivity, capacity and velocity of lithium adsorption as well as stability and durability in a lithium-containing aqueous solution along with low toxicity and outstanding inexpensiveness and a method for the preparation of such an adsorbent.
As is known, metallic lithium and various kinds of lithium compounds are highlighted in recent years as a material useful in a wide variety of applications including, for example, ceramic materials, dry batteries, absorption refrigerants, medicines and so on. It is expected further that the future demand for metallic lithium and lithium compounds will expand to a large extent in the fields of large-capacity batteries, aluminum-based alloys, fuels in nuclear fusion-type reactors and others consequently with a rapid growth of the overall consumption of lithium materials throughout the world.
Natural resources for lithium production are obtained either from the lithosphere or from the hydrosphere. Namely, ores of several kinds of lithium-containing minerals are known on one hand including spodumene, amblygonite, petalite, lepidolite and the like of which the content of lithium is usually in the range from 2 to 6% while, on the other hand, the waters from certain salt lakes and underground brines containing from 50 to 200 ppm of lithium are also useful as a starting material of lithium production.
The occurrence of these natural resources of lithium, however, is localized on the earth so that some countries, e.g. Japan, are entirely devoid of lithium resources totally depending on imported materials for their lithium production and being confronted by a very serious need for developing a route to obtain lithium sources by themselves. A possibility therefor is, for example in Japan, to utilize the naturally occurring watery lithium sources such as certain geothermal underground hot water and hotspring water found in some districts of the country and the sea water available in an infinite volume from the surrounding ocean although the concentration of lithium therein is much lower than in the conventional lithium sources as is only 0.17 ppm in the sea water. Accordingly, the key problem to be solved in this regard is to develop and establish an efficient method for the collection and recovery of the lithium value even from these lithium sources in the form of a low-concentration aqueous solution available in those countries.
Several methods have been proposed for the recovery of the lithium value from a low-concentration aqueous solution of lithium including coprecipitation and adsorption on an adsorbent. For example, a method by the coprecipitation with aluminum hydroxide is proposed in the Preprint I for the 43rd Annual Meeting of the Chemical Society of Japan, page 1240 (1981). The adsorbents for the adsorption of lithium hitherto disclosed include amorphous aluminum hydroxide taught in Kaisui, volume 32, page 78 (1978) and Nippon Kogyokai-shi, volume 99, page 585 (1983), metallic aluminum taught in Bosei Kanri, volume 1982, page 369, hydrated tin oxide taught in Nippon Kogyokai-shi, volume 99, page 933 (1983) and others.
Alternatively, a method for the selective enrichment of lithium in sea water or a salt lake water is taught in Geological Survey Professional Paper, volume 1005, page 79 (1976) according to which the water is concentrated by evaporation utilizing the solar energy to precipitate sodium chloride and other major constituent salts to leave a decreased volume of the mother liquor containing lithium in a relatively increased concentration.
These prior art methods each have their respective disadvantages and problems. For example, the methods by adsorption are generally disadvantageous due to the impractically low capacity and velocity for the adsorption of lithium on the adsorbent from a low-concentration aqueous solution. The method of evaporation utilizing the solar energy is under limitation of the availability of a sufficiently wide area of the plant site and the atmospheric or meteorological conditions in favor of the desired rapid evaporation so that this method is also hardly practicable in countries such as Japan.
To give a more detailed review of the adsorbents for lithium, it is reported that thorium arsenate and tin antimonate have adsorptive power for lithium according to Journal of Inorganic and Nuclear Chemistry, volume 32, page 1719 (1970) and Hydrometallurgy, volume 12, page 83 (1984), respectively, but practical use of these adsrobents still requires improvements in the adsorptivity and development of the method for the desorption of the adsorbed lithium therefrom. Further, Russian investigators have reported in Neorganitscheskii Materialy, volume 9, page 1041 (1973) and volume 12, page 1415 (1976) that various kinds of ion sieve-type adsorbents are useful for the adsorption of lithium although no details are disclosed on the preparation of the adsorbents and the effectiveness thereof for the adsorption of the lithium value in naturally occurring waters.